Implement NEP-17

[shargon]

Related to neo-project/proposals#108 (comment)
Close #2023 #2012
Require neo-project/proposals#124

Version with call flags

[shargon]

using Neo.IO;
using Neo.Ledger;
using Neo.SmartContract.Manifest;
using Neo.VM.Types;
using System;
using System.Linq;
using System.Numerics;
using Array = Neo.VM.Types.Array;

namespace Neo.SmartContract
{
    partial class ApplicationEngine
    {
        public static readonly InteropDescriptor NEP5_EmitTransfer = Register("NEP5.EmitTransfer", nameof(NEP5EmitTransfer), 0, CallFlags.AllowModifyStates, false);

        protected internal void NEP5EmitTransfer(UInt160 from, UInt160 to, BigInteger amount)
        {
            // Send notification

            SendNotification(CurrentScriptHash, "Transfer",
                new Array { from == null ? StackItem.Null : from.ToArray(), to == null ? StackItem.Null : to.ToArray(), amount });

            if (to == null)
            {
                return;
            }

            // Call onPayment method if exists

            ContractState contract = Snapshot.Contracts.TryGet(to);
            if (contract is null)
            {
                return;
            }
            ContractMethodDescriptor md = contract.Manifest.Abi.GetMethod("onPayment");
            if (md is null)
            {
                return;
            }

            ContractManifest currentManifest = Snapshot.Contracts.TryGet(CurrentScriptHash)?.Manifest;
            if (currentManifest != null && !currentManifest.CanCall(contract.Manifest, md.Name))
                throw new InvalidOperationException($"Cannot Call Method {md.Name} Of Contract {contract.ScriptHash} From Contract {CurrentScriptHash}");

            CallContractInternal(contract, md, new Array(ReferenceCounter) { amount }, CallFlags.All, CheckReturnType.EnsureIsEmpty);
        }
    }
}

What do you think?

[erikzhang]

I don't think it's a good idea. We may have a lot of NEPs in the future. Maybe NEP-5 will be obsolete in the future, what shall we do then?

[shargon]

@erikzhang Please take a look again, I added DropResult into CheckReturnType in order to fix the problem with native contracts. Regular smart contracts must call first System.Contract.Exists

[lock9]

Hi Shargon, I noticed that now neo is doing some method checks using hardcoded strings for method names ('verify', for example). I believe this may cause some issues in the future. First 'verify', now 'onPayment'. Maybe the manifest file should have a section to map these methods into ABI methods. This way, instead of checking only if the method exists, you would get the name of it first, and if it exists, execute it.

[shargon]

instead of checking only if the method exists, you would get the name of it first, and if it exists, execute it.

Could you give me an example, i don't see the difference right now. 😕

[ixje]

@lock9

[ProDog]

In neo-project/neo-devpack-dotnet#391, hash has removed from the abi.
So here need to sync

neo/src/neo/SmartContract/Manifest/ContractAbi.cs

Line 48 in 62a3ca2

Hash = UInt160.Parse(json["hash"].AsString()),

in #2044.

[shargon]

@erikzhang Merge before the proposal, or we should wait?

[erikzhang]

We can merge it first. If the proposal changes, we can create another PR.